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Based on the introduction of a dual-loop current control strategy for a grid-connected inverter, an averaged switching model of a grid-connected inverter with an LCL-filter in discrete domain is built under a stationary frame and a proportional resonant (PR) regulator is adopted in the current loop to track the given fundamental sinusoidal current. The impacts of PR parameters, LCL parameters and digital delay on the root locus are studied, respectively. The parameters of the LCL-filter and the PR current regulator loop are designed to assure system stability and dynamic response during a wide power range by using the pole placements method. Finally, a 10 kW prototype of a grid-connected inverter with an LCL-filter is set up to verify the effectiveness, the practicality and robustness of the proposed PR current design method.